U.  S.  WEATHER  BUREAU. 


FOR  USE  OF  THE 


RAIN-GAUGE 


INSTRUCTIONS  FOB  USE  OF  THE  RAIN-GAUGE. 

The  Weather  Bureau  solicits  the  observation  and  record  of  rain, 
snow,  and  hail,  at  carefully  selected  stations,  with  a  three-fold  object: 
to  benefit  commerce  on  navigable  streams,  to  assist  the  operations  of 
agriculture  by  irrigation  and  water  storage  in  regions  where  the  rain- 
fall is  insufficient  at  the  time  when  the  crops  most  require  water,  to 
enable  specialists  of  the  Bureau  to  gain  such  knowledge  of  the  climate 
of  the  several  regions  of  the  country  as  will  permit  them  to  supply 
engineers  and  others  with  the  facts  which  are  needed  to  govern  them 
in  the  construction  of  water  and  other  works.  These  eminently  prac- 
tical benefits  are  to  be  obtained  only  by  carefully  prepared  records  of 
observations  of  the  rainfall  made  at  many  stations.  To  secure  this 
accuracy  each  observer  should  study  the  simple  instructions  herewith 
offered  for  his  guidance. 

1.  Each  station  will  be  equipped  with  a  standard  rain-gauge,  and 
if  possible,  a  wooden  box  support,  complete,  which  is  to  be  mounted 
in  the  manner  described  below. 

The  rain-gauge  consists  of  three  parts — 
The  receiver,  A. 
The  overflow  attachment,  B. 
The  measuring  tube,  C. 

The  top  cylindrical  portion  of  the  receiver,  marked  a  in  Fig.  2,  is 
exactly  8  inches  in  diameter,  inside,  and  is  provided  with  a  funnel- 
shaped  bottom,  which  conducts  any  precipitation  falling  into  the  re- 
ceiver into  the  tall  cylindrical  measuring  tube,  (7,  the  total  height  of 
which,  inside,  is  exactly  20  inches.  The  diameter  of  this  tube  is  much 
smaller  than  the  large  receiving  tube,  a,  being  only  2.53  inches.  In 
consequence  of  this  a  small  amount  of  rain  falling  into  the  receiver  and 
flowing  into  C  fills  the  latter  to  a  depth  greater  than  the  actual  rainfall 
in  proportion  as  the  area  of  the  receiver  is  greater  than  the  area  of  the 
measuring  tube.  In  the  standard  gauges  of  the  Weather  Bureau  the 
depth  of  the  rainfall,  in  accordance  with  this  principle,  is  magnified 
just  ten  times.  The  receiver,  A,  has  a  sleeve,  d,  Fig.  3,  which  slips 
over  the  tube,  (7,  and  very  effectually  prevents  any  loss  of  rainfall. 
Again,  when  the  rainfall  is  very  heavy  the  tube,  (7,  may  be  more  than 


368060 


2 


filled.  In  this  case  to  still  prevent  loss  a  little  opening,  shown  at  e, 
Fig.  2,  is  made  in  the  sleeve,  d,  just  on  a  level  with  the  top  of  the  tube, 
C.  The  excess  of  rainfall  escapes  through  this  opening,  and  is  retained 
in  the  large  overflow  attachment,  J9,  and  can  be  measured  afterwards, 
as  will  be  described  below.  In  the  drawing  the  diameter  of  the  over- 
flow attachment  is  shown  as  less  than  8  inches,  but  in  the  latest  style 
gauges  this  part  is  now  also  made  just  8  inches  inside  diameter.  The 
object  of  this  is  to  be  able  to  use  this  portion  of  the  instrument  as  a 
snow  gauge,  as  will  be  explained  hereafter. 


Fig.I. 
FrontView. 


Fig.  2. 
"Vertical  Section. 


aillllllllllllllli; 


f\ 

A. 

C 

V 

v"T~^ 

X 

d 

— 

d 

B 

C 

RAIN  GAUGE 


Fig.  3. 
Receiver. 


Fig.  4. 
Horizontal  Section,E-F. 


01    23    4     5    6    7    8    9    10   It    12   13  If   15  16   17  IS  19  20  21  22-tt  24  IHCHU. 
SCALE. 

EXPOSURE  OF  RAIN-GAUGES. 

2.  It  is  desired  observers  use  particular  care  in  selecting  a  good 
place  of  observation,  as  the  value  of  the  records  is  sometimes  greatly 


impaired  by  improper  exposure.  It  is  scarcely  necessary  to  say  that 
every  precaution  should  be  taken  to  protect  gauges  from  the  inter- 
ference of  animals  and  unauthorized  persons.  Select,  if  possible,  a 
position  in  some  open  lot  as  unobstructed  as  possible  by  trees,  build- 
ings, or  fences.  Such  a  place  in  general  affords  the  best  exposure, 
though  sometimes  difficult  to  find.  Gauges  should  be  exposed  upon 
roofs  of  buildings  only  when  necessary,  and  then  the  roof  should  be 
flat,  or  nearly  so,  if  possible.  The  middle  portion  of  a  flat  unobstructed 
roof  generally  gives  the  best  results. 

RAIN-GAUGE  SUPPORT. 

3.  The  box  in  which  the  gauge  is  shipped  to  the  observer  is  expressly 
designed  as  a  stand  for  the  instrument,  and  should  be  opened  at  the 
head,  which  is  fastened  by  screws.     Set  the  box  up  as  nearly  vertical 
as  possible  at  the  place  selected  for  the  exposure  and  ballast  by  filling 
the  lower  portion  with  several  inches  of  stone  or  broken  brick.     Slip 
in  the  head  and  lower  to  the  level  of  the  screw  holes  in  the  sides  of  the 
box  about  10  inches  from  the  bottom,  where  the  head  is  securely  fastened 
with  the  screws  taken  out  in  opening  the  box.     The  support  is  further 
secured  and  fixed  in  its  position  by  piling  up  a  few  stones  around  the 
outside.     The  gauge  can  now  be  placed  inside  and  appears  as  shown  in 
the  drawing. 

TO  MEASURE  RAINFALL  AND  SNOWFALL. 
BAINFALL. 

4.  The  rain-gauge   measuring  stick  is  graduated  into  inches  and 
tenths  of  inches.     Remembering  that  the  actual  depth  of  the  rainfall  is 
magnified  ten  times,  as  explained  above,  it  is  plain  that  if  we  find  the 
water  10  inches  deep  in  the  measuring  tube,  then  the  real  rainfall  must 
have  been  only  one  inch  deep,  or,  if  the  water  in  the  tube  is  only  one- 
tenth  inch  (or  written  as  a  decimal  .1  inch)  deep,  then  the  rainfall 
must  have  been  only  one  one-hundredth  inch  (or  written  as  a  decimal 
.01  inch). 

5.  To  save  observers  the  trouble  of  always  thinking  about  the  mag- 
nification, and  to  avoid  possible  errors  in  reports,  the  numbers  on  the 
graduation  of  the  measuring  sticks  are  not  actual  inches,  but  in  the 
latest  pattern  of  measuring  sticks  have  all  been  divided  by  10,  and  thus 
represent  the  actual  rainfall.     Moreover,  these  numbers  are  expressed 
in  hundredths  of  inches  of  rainfall,  and  are  written  as  decimal  fractions. 
Thus  the  ten-inch  line  is  numbered  1.00  (read  one  and  zero  hundredths), 


which  is  the  depth  of  rainfall  in  inches  corresponding  to  10  inches  of 
water  in  the  measuring  tube  ;  similarly  the  one-inch  line  is  numbered 
.10  (read  ten  one-hundredths),  which  again  is  the  depth  of  rainfall  in 
inches  corresponding  to  one  inch  of  water  in  the  tube. 

6.  The  depth  of  the  water  is  measured  by  inserting  the  measuring 
stick  into  the  gauge  through  the  small  hole  in  the  funnel.     When  the 
stick  reaches  the  bottom  of  the  measuring  tube  it  should  be  held  for 
one  or  two  seconds  and  then  quickly  withdrawn  and  examined  to  see 
at  what  division  of  the  graduation  the  top  of  the  wetted  portion  comes. 
The  numbering  of  this  division,  as  stamped  on  the  stick,  gives,  as  has 
just  been  explained,  the  actual  depth  of  rainfall,  and  in  making  out 
records  and  reports  observers  should  always  use  the  decimal  expressions. 
Of  course,  it  will  rarely  happen  that  the  top  of  the  wetted  portion  will 
fall  exactly  upon  one  of  the  numbered  lines — it  will  generally  be  on  or 
near  one  of  the  shortest  lines.     Thus,  for  example,  suppose  the  water- 
mark comes  to  the  sixth  short  line  beyond  the  line  numbered  .80, 
the  proper  record  to  make  in  this  case  would  be  .86  inch  rainfall. 
The  number  of  short  lines,   reckoned  from  the  numbered  line  next 
lower,  are  always  to  be   inserted  in  place  of  the  0  in  the  stamped 
numbers. 

7.  Observers  should  always  be  careful  to  put  the  stick  into  the  gauge 
so  that  the  end  at  which  the  numbering  begins  goes  to  the  bottom,  and 
the  stick  passes  through  the  middle  of  the  tube  ;  for  if  the  stick  is 
placed  near  the  sides  the  water  is  sometimes   drawn  up  by  capillary 
action  in  the  narrow  space  between  the  stick  and  the  tube,  so  as  to  wet 
the  former  entirely  too  high  and  give  very  erroneous  records. 

8.  After  measuring  and  recording  in  this  way  the  precipitation  found 
in  the  gauge  the  top  should  be  removed,  the  measuring  tube  emptied 
and  drained,  and  the  gauge  put  in  position  again.     Observers  should 
be  careful  after  emptying  the  gauge  to  replace  the  measuring  tube  so 
that  the  bottom  stands  within  the  ring  in  the  middle  of  the  bottom  of 
the  overflow,  and  in  putting  on  the  receiver  that  it  passes  over  the 
measuring  tube  and  rests  squarely  down  upon  the  overflow. 

9.  When  the  amount  of  rain  that  has  fallen  more  than  fills  the  measur- 
ing tube,  the  total  rainfall  is  determined  in  the  following  manner : 
First  carefully  remove  the  receiver  so  as  not  to  spill  any  of  the  water 
in  the  measuring  tube,  which  should  be  exactly  full ;  the  latter  is  then 
slowly  and  carefully  lifted  out  so  as  not  to  spill  any  of  the  water  into 
the  overflow,  emptied  and  allowed  to  drain  a  moment  or  so  ;  the  water 


6 

remaining  in  the  overflow  is  now  poured  into  the  measuring  tube,  being 
careful  not  to  lose  any,  and  measured  in  the  usual  way.  Suppose  we 
find  this  to  be  .47  inch  rainfall,  then,  remembering  that  the  measur- 
ing tube  is  just  20  inches  high,  the  total  rainfall  will  be  2  inches  plus 
.47  inch  zz  2.47  inches. 

SNOWFALL. 

10.  During  the  winter  season,  especially  in   those  climates  where 
the  precipitation  is  nearly  all  in  the   form   of  snow,  it  is  necessary  to 
have  only  the  overflow  attachment  exposed  in  the  support  as  a  snow- 
gauge,  removing  the   receiver  and   measuring  tube  to   the  house  as 
these  parts  cannot  be  used  for  measuring  snow,  and  even  if  rain  should 
occur  it  is  very  apt  to  be  frozen  while  in  the  measuring  tube,  generally 
bursting  it  and  rendering  it  worthless  or  highly  inaccurate. 

11.  The  snowfall  collected  in  the  overflow  attachment  is  measured 
by  first  placing  the  vessel  in  a  warm  room  until  the  snow  is  melted. 
The   water  is  then   carefully  poured  into  the   measuring  tube   and 
measured  just  as  though  it  were  rainfall. 

12.  In  addition  to  this  measurement  by  the  gauge  a  measurement 
will  be  made  of  the  actual  depth  in  inches  of  the  snow  on  the  ground. 
Select  a  level  place  of  some  extent  where  the  drifting  is  least  pro- 
nounced and  measure  the  snow  in  at  least  three  places.     The  mean  of 
these  measurements  will  give  the  snowfall  which  is  to  be  entered  in 
the  f  Mirth  column  of  the  report,  and  whenever  it  is  impracticable  to 
melt  the  snow  as  described  in  the  preceding  paragraph,  one-tenth  of 
this  mean  will  give  an  approximate  value,  in  water,  for  the  snow  which 
could  not  be  melted.     This  value  must  be  set  down  in  the  third  column 
of  the  report  in  precisely  the  same  manner  as  rainfall,  or  snow  melted 
in  the  gauge.     After  having  once  made  a  measurement  of  the  snowfall 
it  is  not  desired  that  the  same  snow  be  measured  at  each  succeeding 
observation  until  it  shall  finally  disappear.     Any  fresh  snow,  however, 
should  be  measured  and  recorded  as  it  falls.     If  there  be  any  snow  on 
the  ground  at  the  end  of  the  month  that  fact  and  the  depth  in  inches 
should  be  noted. 

13.  Observations  should  be  made  every  evening,  also  at  the  close  of 
every  storm,  and  the  gauge  should  be  emptied  of  all  the  water  it  may 
contain  as  soon  as  it  has  been  measured. 

14.  The  form  supplied  for  these  records  will  be  found  self-explana- 
tory.    Rainfall  observers  will  disregard  the  columns  headed  "  Tem- 
perature," but  should  confine  their  attention  to  those  headed  "Pre- 


cipitation."  The  first  and  second  columns  have  to  do  with  the  time 
of  beginning  and  ending  of  the  storm  and  together  measure  its  dura- 
tion. In  the  third  column  is  to  be  entered  the  reading  of  the  gauge,  as 
described  in  sections  4,  5,  and  6  of  these  instructions.  If  no  rain, 
snow,  or  hail  has  fallen  during  the  period  of  observation  make  the 
entry  .00,  or  u  No  precipitation,"  in  this  column.  If  the  amount  is  too 
small  to  measure  make  the  entry  " Trace."  The  fourth  column  is 
provided  for  the  record  of  snow  measurements  made  by  the  method 
described  in  section  12.  In  the  " Monthly  summary"  all  matters 
indicated  are  proper  subjects  of  the  rainfall  observer's  record,  with  the 
exception  of  the  three  lines  which  deal  with  temperature. 

15.  It  is  particularly  important  in  the  interests  of  accuracy  that  the 
observations  be  recorded  as  soon  as  made,  and  that  the  daily  entries 
be  made  day  by  day.     The  forms  for  each  month  should  be  mailed  on 
the  first  day  of  the  succeeding  month.     Even  if  no  rain  has  fallen  the 
observer  should  bear  in  mind  that  his  official  record  of  that  fact  is  as 
important  as  though  it  were  a  month  of  rain. 

16.  Requisition  for  blank  forms  or  envelopes  may  be  made  at  any 
time,  and  will  receive  immediate   attention.      It  is  not  necessary  to 
write  a  letter  asking  for  them,  a  simple  note  on  the  margin  of  the 
monthly  report  will  be  sufficient. 


Gaylord  Bros. 

Makers 
Syracuse,  N.  Y. 

PAT.  JAN.  21,  1908 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


